This invention relates to a hydraulic elevator drive system wherein fluid control means regulates the fluid within a hydraulic actuator operatively controlling the movement of an elevator car.
Hydraulic elevator systems have commonly employed one or more valves for controlling the supply of fluid to and from a hydraulic actuator such as a jack or the like to thereby control movement of an elevator car for transporting load, such as passengers, for example, between a plurality of landings within a building structure. Such valving structure has been selectively operated in conjunction with a hydraulic pump for selectively supplying fluid under pressure to the hydraulic jack for raising the elevator car. Likewise, valving structure has been selectively controlled to vent the control fluid from the hydraulic jack for permitting the car to descend.
The use of an integrated valve structure containing a plurality of control valves has been found to be highly desirable for interconnecting a fluid pump, a fluid reservoir and the actuating jack to control both upward and downward movements of an elevator car. One desirable system is shown in the U.S. Pat. No. 3,508,468, issued on Apr. 28, 1970 and assigned to a common assignee herewith, which employs a by-pass valve functioning with a check valve for selectively controlling the flow of fluid from a pump to an actuating jack or cylinder while a bleed valve interconnects the actuating jack or cylinder with a reservoir for controlling downward movement of the car.
Another known system employs a first valve and valve operator to interconnect a fluid pump with an actuating jack which functions as a combined check and lowering valve while a second valve and associated valve operator interconnects the pump with a reservoir, such as shown in the U.S. Pat. No. 2,737,197, issued on Mar. 6, 1956. The control apparatus in the U.S. Pat. No. 2,737,197 provides variable upward control by varying the opening of the by-pass valve and variable downward control by varying the check and lowering valve.
Some known systems have regulated the positioning of a lift platform or the like by generating an electrical position responsive signal which is compared with a commanded positioned signal for generating a position error control signal, such as shown in the U.S. Pat. No. 3,570,243, issued on Mar. 16, 1971, which controls a hydraulic pump motor operation to vary the fluid flow to the hydraulic lift actuator.
The speed of a lift or elevator has been controlled by regulating the amount of fluid flow to or from a hydraulic actuator or jack through the selective positioning of one or more valves. One known system selectively positions and regulates the movement of a deck edge elevator on the side of a ship, such as shown in the U.S. Pat. No. 2,409,198, issued on Oct. 15, 1946, by selectively positioning a control valve in response to a mechanical differential responsive to the speed of an operating plunger and to the speed of an electric motor.